The present invention relates to an apparatus for fluid-bed drying, particularly for simultaneous drying and disintegration of a material in the form of a paste, said apparatus having a cylindrical drying chamber with a conical bottom in fixed connection therewith, and having a rotating stirrer placed coaxially in the drying chamber, the blades of said stirrer being parallel to the conical bottom, and having members for the supply of material to be dried, and also apertures for the supply and removal of the medium for fluidization and drying and for the removal of the dried product.
From Denmark PS No. 130,338 an apparatus is known which produces a rotating floating layer, and which is substantially of the nature mentioned in the introduction, the bottom of said apparatus being narrowed conically downwards, and the fluidization medium being introduced from below through a slit between the wall in the conical bottom and a rotating disc carrying the stirrer blades. It has been explicitly mentioned in the patent specification that the apparatus makes it possible to use fluidization technique, i.a. in the processes of treating pastes.
By the drying of materials in the form of a paste in such a known apparatus a certain portion of the material in larger and smaller moist particles will occur already at their introduction into the drying chamber, the larger particles preferably making for the lowermost part of the fluidized layer in the conical bottom, where the velocity of the drying air will be highest on account of the shape of the bottom. This results partly in a powerful drying of the surfaces of these particles, and partly in a disintegration of the particles caused by the collision between the particles and the rotating blades.
However, in the said apparatus this process is rather incomplete, because, as mentioned, the drying air is introduced, through a slit between the stirrer disc and the wall in the bottom, so that the particles are liable to collect near the middle of the conical bottom and be deposited on the disc near its axis of rotation.
In a further development of such an apparatus a drying chamber with a substantially flat bottom and a stirrer has been used for the drying of materials in the form of a paste. In this case, the stirrer blades extend parallel to the axis of the drying chamber, the drying air being introduced into the chamber through a series of vertical slits at the bottom of the chamber distributed over its circumference. Also by this construction the larger moist particles are liable to be deposited on the bottom of the drying chamber near its axis. A somewhat similar construction is the subject of German DE-OS No. 28 53 913, which deals with an apparatus for the drying of synthetic textile fibres, the drying air being introduced tangentially into the drying chamber at one side of a downwardly arched bottom, above which a stirrer has been provided.
Finally, from U.S. Pat. No. 2,761,769 an apparatus for fluidized catalysis is known, having in a cylindrical chamber a rotating, upwardly conical, perforated bottom, through the perforations of which the fluidization medium is supplied. It is true that by this construction it is obtained that the material will not show any tendency to collect or be deposited at the axis of the chamber, but this apparatus is quite unsuitable for simultaneous drying and disintegration of materials in the form of a paste, as no conditions exist therein which may lead to a disintegration of the larger particles.